Servo modification comparison

Tim M.

This may be a dumb question, but i was considering my options earlier about modifying some newly acquired servos.· They are just standard Futabas.· In the past, i've just clipped the stopper, and centered the POT.· That worked good for a while, but they would always need re-adjusting.· I really dont like the idea of using superglue to hold the pot in place.· My question is about using a pair of 2.2k resistors to replace the pot.· I read how to do it, but it didnt give any information on it about after you do it.· Is doing that pretty much the same as it was with a centered pot, only it will never go out of adjustment?· If so, that'd be the way i want to go.· I'd like to hear from a couple people that may have tried it both ways, and see which you prefer.
Thanks
-Tim

allanlane5

I'd recommend hot-glue, instead of the superglue.

With hot-glue, you get a flexible bond, which can be removed later.

Using 2 x 2.2 Kohm resistors should give you a standard 'center' pulse-width, but it will NOT be an adjustable 'center'. And, since resistors are usually +- 10%, or +- 5%, it may be slightly different for each servo you modify. If you pursue this, select your resistors with an ohm-meter, to get two resistors that are as close to each other in value as you possibly can.

Over temperature (0 to 70 degrees) they may still vary differently from each other, but at least you have a chance.

Martin_H

I read and used a technique where you file a notch in the top of the pot shaft. This allows you to trim the center by removing the screw from the spline and sticking a fine screw driver into the hole to turn the pot. This worked great and allows for later trim adjustment as required.

RobotWorkshop

I have a slightly different method.....

I enlarge the notch where the wires come out of the servo and then relocate the pot outside the servo. Some servos like Airtronics have the pot attached by three wires so I just pull the whole thing out of the servo. For others just use a strip of three wires pulled from a ribbon cable and solder it to the pot and board.

With that you can do all the adjustments outside the servo and easily readjust if required.

Robert

erco

Alternatively, you could replace the standard pot with a 10-turn trimpot. Radio Shack has 10K units which would probably work fine (your post implies that the standard pot is 5K). With a trimpot, you could leave the existing pot in place, routing the 3 pot wires through the case (as Robert suggested) and attach the small rectangular trimpot to the servo with CA or hot glue. A 10-turn trimpot provides much finer adjustment and is much less likely to vibrate out of position, compared to the standard 3/4 turn pot.

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·"If you build it, they will come."